Should I use a comma before an opening quotation mark?
When you include quoted material or dialogue in a sentence then you should proceed it with a comma unless it fits into the flow of the sentence seamlessly, e.g. The President said that there is "no smoking gun" to be found.
In these cases, the sentence would be syntactically correct without the quotation marks, and you are just using the quotation marks to show that the quote is a direct quote. Often, in this scenario, the quote will be preceded by "that", e.g. He said that "the country will continue to grow."
Otherwise, you should use a comma before opening quotation marks, e.g. Sandra called out, “What do you want from the store?”